This application is based on Japanese Patent Application No. 9-361503 (1997) filed Dec. 26, 1997 and Japanese Patent Application No. 10-356583 (1998) filed Dec. 15, 1998, the contents of which are incorporated hereinto by reference.
The present invention relates to a recording apparatus and a recording method and more particularly to a recording apparatus and a recording method that performs recording on a recording medium by scanning the recording medium while ejecting ink from a recording head.
A recording apparatus connected to a computer can record or print an image on paper according to image data generated by the computer. Various types of printers have been devised including a dot impact type, a heat transfer type and an electrophotographic type. In recent years, an inkjet type has prevailed. The inkjet printer achieves printing by ejecting ink from the recording head and therefore can print on recording mediums with unsatisfactory surfaces including, for example, rough plain paper, leather and cloth as long as they can absorb ink.
A serial printer in particular, which comprises, in its basic configuration, a paper feeding mechanism, a head scan mechanism, a motor drive circuit, a head drive circuit, a data processing/control circuit, an operation/display circuit and a power supply circuit, has a simple construction as compared with a printer of the electrophotographic type such as a laser beam printer (LBP) that is in wide use at offices. Currently, the serial inkjet printer is widely used in small offices and homes as a popular, low-cost printer.
Here, a conventional commonly used inkjet printer is explained. Data entered from a computer into an input terminal is stored in a buffer of a signal processing circuit and converted into data corresponding to individual nozzles of the recording head. The converted data is transferred via a flexible cable to a head drive circuit on a carriage where it is converted into a signal for driving a heater of the recording head. The head drive circuit generates pulses in synchronism with the moving position of the carriage to eject ink. The position of the carriage can be obtained from a signal that is produced by reading the output of a linear encoder extending along the scan direction of the carriage or from a drive pulse for a carriage driving pulse motor.
When the printer receives data from the computer, a sheet of paper set in a paper supply unit is conveyed to the paper feeding mechanism. The recording head mounted on the carriage performs recording on the paper in a range corresponding to the head recording width. After recording is finished for one scan, the paper feeding mechanism feeds forward the paper by a distance equal to the recording width. The scanning and paper feeding are repeated as far as the paper can be fed, after which the paper is discharged from a discharge port.
Although the serial inkjet printer is relatively simple in construction, because the recording head scans and performs recording for each line, any misregistration or misalignment between the lines will clearly show in the printed image. Because the inkjet printer in particular ejects ink droplets onto the paper, the paper swells with ink and expands in a planar direction, causing dots near the joint between printed lines to be shifted out of alignment to a greater extent.
The increased misalignment between the lines results from the fact that the recording is performed by ink droplets landing on the paper, ejected from the nozzles of the recording head. The ink droplets that have landed on the surface of the paper penetrate into the interior of the paper where they are fixed. During this process, the water contained in the ink is soaked in the paper thereby swelling the paper. The swelling is not significant with films and paper with special coating. Plain paper, such as copy paper, swells easily. Our experiments show that when struck with 19.3 nl/mm2 of ink, copy paper of one kind produced an elongation of about 0.51%. Generally, paper, after being printed, is restrained in position in the planar direction by spurs 5 as shown in FIG. 1, so that the swelled paper 2 is deformed like a wave over a flat platen 3 between the spurs 5 which are arranged at equal intervals in the scan direction. According to our calculations, when an undulation (hereafter referred to as cockling) occurs at four equally spaced locations in the longitudinal direction of A4 size paper (210 mm), for example, the surface of the recording medium is cockled by about 1.2 mm in the vertical direction as a result of the 0.5%-elongation in the planar direction. The effect of the cockling thus produced in one line shows when the next line is printed.
The ejection timing of ink droplets has conventionally been controlled on the assumption that the distance between the nozzles of the recording head and the paper (hereafter referred to as a paper-nozzle distance) is always constant and that the landing points on the surface of the recording medium are always determined by only the position of the nozzles. In reality, however, the ink landing point on the surface of the paper 2 does not coincide, for the reasons mentioned above, with the carriage position when the ink droplet is ejected, as shown in FIG. 2.
In FIG. 2, X represents the direction of scan and the broken line arrow represents the locus of an ink droplet when recording is performed at the conventional ink ejection timing. If the paper 2 on the platen 3 is not swelled, as shown by the broken line, the paper-nozzle distance remains unchanged and the ink droplet adheres on the position a. When, however, the paper 2 is swelled, it is deformed as shown by the solid line toward the carriage 9, changing the paper-nozzle distance, with the result that the ink droplet adheres on the position b. When there are changes in the paper-nozzle distance as caused by the cockling of the paper 2, dot positions may deviate in the planar direction as mentioned above if the ink is ejected in synchronism only with the carriage position.
It is therefore an object of the invention to control the ink ejection timing based on an information on deviation of the recording medium from the reference value of the distance between the recording medium and the ink nozzle portion of the recording head, that ejects ink droplets onto the recording medium, to correct the ink landing positions on the recording medium and thereby produce a printed image with no dot position deviations.
To improve the above-mentioned object, a recording apparatus and a recording method of the invention are presented. The recording apparatus comprises a recording head for ejecting ink onto a recording medium, a scanning means for moving the recording head in a predetermined direction to scan the recording medium and a correction means for controlling an ejection timing of the ink according to discrepancy information on the recording medium. The discrepancy information on the recording medium represents a deviation of a paper-nozzle distance from a reference value, the paper-nozzle distance representing a distance from a nozzle portion of the recording head to the opposing recording medium.
The recording method ejects an ink on a recording medium, by using a recording head provided with an ejection portion for ejecting the ink, and scans the recording medium by the recording head to perform recording on the recording medium. Moreover, the recording method comprises a step of obtaining discrepancy information on a deviation of a distance from the ejection portion of the recording head to the opposing recording medium, in a scan region of the recording head, and a step of controlling an ink ejection timing of the recording head according to the discrepancy information.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.